1. Field of the Invention
The present invention relates to a cooling structure for a semiconductor device used for an inverter and a regenerative converter that control motors of electric vehicles and trains, for example.
2. Description of the Background Art
In a semiconductor device, a direct-cooled cooling structure in which cooling fins are provided on a lower surface of a base plate on which semiconductor elements are mounted is a structure in which sealing is performed to a jacket through a sealing structure. To equalize flow velocity of refrigerant flowing through the cooling fins, a structure is common in which a header causing the refrigerant flow in the cooling fins is provided on an inflow side and an outflow side of the refrigerant in the cooling fins, in other words, horizontal to the cooling fins.
When the semiconductor elements are mounted on the jacket through the base plate, not only the region of the base plate in which the cooling fins are formed but also the region in which the header is disposed needs to be sealed. Thus, the base plate in larger size than the region in which the cooling fins are formed is used.
Semiconductor devices are conventionally configured as described above, so that although semiconductor elements are minimized, reducing size of base plates is difficult. Thus, miniaturization of semiconductor devices is difficult.
Moreover, in a case where semiconductor devices are mounted on a vehicle, there are restrictions on pressure loss in cooling system of each device, and for example, a cooling structure in a semiconductor device is required to have pressure loss of 10 kPa or less when flow amount of refrigerant is 10 L/min. In order to reduce the semiconductor device in size while satisfying the restrictions, a header is needed to be reduced in size or to be removed. Consequently, pressure loss increases, whereby flow amount of the refrigerant fails to increase.
Furthermore, the header lacks capacity, so that equalizing flow velocity of the refrigerant flowing through the cooling fins is insufficient, which may lead to deterioration of cooling performances. For the reasons as mentioned above, reducing semiconductor devices in size has been difficult.
For example, Japanese Patent Application Laid-Open No. 2008-172024 discloses a structure providing a header on a lower side of cooling fins. In this structure, the header is provided on the lower side of the cooling fins, so that a base plate can be reduced in size, resulting in miniaturization of a semiconductor device.
The structure, disclosed in Japanese Patent Application Laid-Open No. 2008-172024, provides a partition wall that forms the header and a flow path in a jacket. However, undercut portions are generated on a periphery of the partition wall in a process of the jacket, whereby workability of the jacket deteriorates.